Moss Turf Research Articles

Changes in Element Concentrations in Moss Segments After Cross-Transplanting Between a Polluted and Non-Polluted Site

To test the ability of Hylocomium splendens segments to retain absorbed heavy metals (Fe, V and Pb) and some physiological elements (Ca, Mg and K) over a period of some years, moss turf was cross-transplanted between polluted and background sites. Thereby it was possible to determine how quickly the concentrations in moss can reach chemical equilibrium with the atmospheric inputs. At a particular site (background or polluted), the physiological elements in transplanted material quickly reached the levels in the non-transplanted moss. For the heavy metals, the concentrations remained stable over 3 years in moss cross-transplanted from a polluted to a background site. There appeared to be inherent differences between moss at the background and polluted sites in the ability to absorb and accumulate heavy metals.

DNA damage and photosynthesis in Antarctic and Arctic Sanionia uncinata (Hedw.) Loeske under ambient and enhanced levels of UV‐B radiation

AbstractThe response of the bipolar moss Sanionia uncinata (Hedw.) Loeske to ambient and enhanced UV‐B radiation was investigated at an Antarctic (Léonie Island, 67°35′ S, 68°20′ W) and an Arctic (Ny‐Alesund, 78°55′ N, 11°56′ E) site, which differed in ambient UV‐B radiation (UV‐BR: 280–320 nm) levels. The UV‐BR effects on DNA damage and photosynthesis were investigated in two types of outdoor experiments. First of all, sections of turf of S. uncinata were collected in an Arctic and Antarctic field site and exposed outdoors to ambient and enhanced UV‐BR for 2 d using UV‐B Mini‐lamps. During these experiments, chlorophyll a fluorescence, chlorophyll concentration and cyclobutyl pyrimidine dimer (CPD) formation were measured. Secondly, at the Antarctic site, a long‐term filter experiment was conducted to study the effect of ambient UV‐BR on growth and biomass production. Additionally, sections of moss turf collected at both the Antarctic and the Arctic site were exposed to UV‐BR in a growth chamber to study induction and repair of CPDs under controlled conditions. At the Antarctic site, a summer midday maximum of 2·1 W m−2 of UV‐BR did not significantly affect effective quantum yield (ΔF/Fm′) and the ratio of variable to maximal fluorescence (Fv/Fm). The same was found for samples of S. uncinata exposed at the Arctic site, where summer midday maxima of UV‐BR were about 50% lower than at the Antarctic site. Exposure to natural UV‐BR in summer did not increase CPD values significantly at both sites. Although the photosynthetic activity remained largely unaffected by UV‐B enhancement, DNA damage clearly increased as a result of UV‐B enhancement at both sites. However, DNA damage induced during the day by UV‐B enhancement was repaired overnight at both sites. Results from the long‐term filter experiment at the Antarctic site indicated that branching of S. uncinata was reduced by reduction of ambient summer levels of UV‐BR, whereas biomass production was not affected. Exposure of specimens collected from both sites to UV‐BR in a growth chamber indicated that Antarctic and Arctic S. uncinata did not differ in UV‐BR‐induced DNA damage. It was concluded that S. uncinata from both the Antarctic and the Arctic site is well adapted to ambient levels of UV‐BR.

The Effect of Polytrichum piliferum on Seed Germination and Establishment on Iron Mine Tailings in New York

Seedling establishment on iron mine tailings in New York State's Adirondack Park was studied to determine if cover by the bryophyte Polytrichum piliferum Hedw. facilitated or inhibited seed germination and seedling survival, relative to other substrates present on the site. The occurrence of vascular vegetation on the four most commonly occurring substrates (bare tailings, cryptogamic crust, grass litter, and Polytrichum piliferum) was compared. An association survey detected preferential association between vascular vegetation and cover of Polytrichum piliferum, particularly for winter annual and biennial species. Seeds of Panicum virgatum L. and Melilotus officinalis (L.) Pallas were experimentally sown onto the four natural substrates, as well as on artificial substrates designed to mimic bryophyte turf. Germination on Polytrichum turf exceeded that of other substrates. However, seedling survivorship was low on all substrates, with no seedling surviving past 13 wk. Shade treatment on natural substrates significantly increased germination and somewhat extended survival. The results suggest that Polytrichum cover acts as a safe site for species that germinate and establish in cooler weather. However, even experimental shading of moss turf does not ameliorate summer heat stress sufficiently to permit establishment of seeds that germinate in early summer.

Extreme Leaf Dimorphism in Calymperaceae

Constant extreme leaf dimorphism in the moss family Calymperaceae, involving evolution of the gemmiferous leaf of some species into a rod-like essentially naked costa or a narrow tube-like or channeled shaft, occurs more or less consistently in five species of Calymperes and six species of Syrrhopodon world wide (approximately eight percent of the species of the family), but not in the closely related genus Mitthyridium. Such highly derived gemmiferous leaves—referred to here as stenophylls—are an evolutionary phenomenon that is not known for any other group of mosses. The stenophylls bear the gemmae on their tips, are rigidly erect both wet and dry, are generally longer than and mostly have smaller areas of cancellinae than the vegetative leaves. The principal functional-evolutionary benefit of this type of extreme leaf dimorphism may be the constant (plants hydrated or desiccated) presentation of the gemmae for dispersion elevated above the potentially trapping tangle of vegetative leaves of the moss turf. Also, some of the stenophylls can store water transiently in tubes or channels. The stenophylls presumably play only a minor role in photosynthesis due to their lack or near lack of green lamina; thus reduction of overall photosynthetic area per plant is a consequence of strongly expressed specialization for asexual reproduction in these dioicous mosses. Likewise, reduction in water-retaining capacity per plant is a consequence of reduction in area of the cancellinae of stenophylls. Four of the extreme leaf-dimorphic Calymperes species occur in Malesia and one in tropical America; one of the extreme leaf-dimorphic Syrrhopodon species occurs in Malesia, three in tropical America, one in eastern North America, and one in eastern Africa (including the island of Mauritius).

Uptake of Ca, Mg and K during growth of annual segments of the moss Hylocomium splendens in the field

The transfer of Ca, Mg and K between annual segments of Hylocomium splendens and from the underlying organic substratum was investigated in a cross-transplant study. Samples of moss turf only, moss turf plus the organic layer, and organic layer only, were cross-transplanted between a Ca- and Mg-contaminated site close to a lime factory and at an uncontaminated site. During a relatively dry autumn, when growth in biomass was not evident, acropetal transfer of Mg, but not of Ca, from the brown and decaying moss segment was evident. In the subsequent winter to spring period, aerial supply appeared to dominate uptake of Ca and Mg to growing segments. In lime-contaminated moss segments transplanted to the uncontaminated site, Ca and Mg were tightly retained in the green segments, presumably by transfer between old and new tissue, with no evidence of leaching to achieve new chemical equilibria with the environment.

Biological and environmental characteristics of three cosmopolitan mosses dominant in continental Antarctica

Abstract. Bryum argenteum, B. pseudotriquetrum and Ceratodon purpureus are the predominant mosses in Victoria Land, continental Antarctica. All have cosmopolitan distributions and are widespread throughout Antarctica with wide ecological amplitudes resulting in considerable morphological variation. They are well adapted to tolerate the physiological stresses imposed by the severe environment. This study investigates aspects of their growth, physiology and survival in response to habitat constraints, especially hydrology. Their distribution is controlled almost exclusively by moisture availability. Each species tends to predominate in a specific zone along hydrological gradients, with B. pseudotriquetrum on moist soil, C. purpureus on drier soil, and B. argenteum on unstable stream margins, fluvial deposits and the marginal capillary zone. Where conditions are optimal, each species can form a turf 6–10 cm thick. Nutrient status of the soil does not appear to be an important determinant in the distribution pattern within communities. The thermal regime of the moss turf varies according to its moisture content; for a period of ca. six weeks during the summer, with the frequent long spells of 24‐h sunshine, temperatures remain above 0 °C for much of the time even though air temperatures are frequently below the freezing point. This allows growth and metabolic activity to proceed continuously at a relatively rapid rate for quite long periods. Annual shoot incremental growth can exceed 3.5 mm in each species. Growth of B. argenteum may be inhibited by UV‐ B radiation. The optimal temperature for photosynthesis in each species is around 15 °C, but significant carbon fixation occurs at 5 °C. Photosynthetic rates at 5, 10 and 20 °C were B. argenteum > B. pseudotriquetrum > C. purpureus.

Architecture, Anatomy, and Functional Morphology of the Pseudopetiolate Species of Calymperes and Syrrhopodon (Musci, Calymperaceae)

World-wide, three species of Calymperes and two of Syrrhopodon (Musci, Calymperaceae) share the foliar feature of a pseudopetiole. This structure, which is unique among mosses, is an interval of naked costa connecting the summit of the leaf base (with its waterretaining cancellinae) to the proximal end of the expanded photosynthetic upper lamina. The primary function of the pseudopetiole appears to be that it elevates and exposes the photosynthetic portion of the leaf above the moss turf In two of these mosses the pseudopetioles form a cagelike system between the leaf bases and the expanded portions of the laminae which functions to retain water for brief periods. The basic functional morphology of the highly derived plants of the moss family Calymperaceae is focused on capture and retention of water. The evolution of the pseudopetiole-a petiole-like interval of naked costa between the leaf base and the upper lamina (Fig. 1)-in five species of these mosses is of considerable interest as an example of extreme specialization in this largely tropical and largely corticolous family. Reese and Tan (1983) presented an overview of what they referred to as the petiolate Calymperaceae. They described and illustrated the condition as they observed it in four species of Calymperaceae, but did not offer suggestions as to the presumed evolutionary origins or possible functions of the pseudopetioles. One purpose of the present article is to add a fifth species-Syrrhopodon aristifolius-to the roster of pseudopetiolate Calymperaceae and to describe features of the condition in greater detail than presented by Reese and Tan. In addition, suggestions are offered for the functional roles of the pseudopetioles. Some considerations possibly bearing on the evolutionary origin of the pseudopetiolate condition are also noted. The mosses discussed in this article occur in two of the three genera of the Calymperaceae. They comprise the paleotropical species Calymperes aeruginosum Sande Lacoste, C. robinsonii Tan & Reese, Syrrhopodon aristifolius Mitten, and S. loreus (Sande Lacoste) Reese, and the neotropical C. venezuelanum (Mitten) Pittier. See Figure 1, and Eddy (1990), Reese and Tan (1983), and Reese et al. (1986) for illustrations of these mosses. It is doubtless noteworthy that pseudopetioles are not known in Mitthyridium, the most highly derived taxon of the Calymperaceae, which is confined to the paleotropics and closely related to Syrrhopodon. There are degrees of the pseudopetiolate condition. For example, not all specimens of C. aeruginosum and S. aristifolius are obviously pseudopetiolate, but some populations of these species are remarkable for strong development of the pseudopetioles. In some collections of both species the plants may have the leaves mostly lacking pseudopetioles, but in other collections the reverse may be true. On the other hand, populations of species such as C. robinsonii, C. venezuelanum (Fig. 1), and S. loreus seem to be rather uniformly pseudopetiolate. The pseudopetioles vary in length among and within the species: C. aeruginosum, 0.0-1.2 mm; C. robinsonii, 1-3 mm; C. venezuelanum, 2-3 mm; S. aristifolius, 0.0-5 mm; S. loreus, 2-5 mm. Specimens of morphologically similar species of Calymperaceae e.g., C. lonchophyllum Schwaegrichen, C. serratum A. Braun, and S. croceus Mitten, often show an approach to the pseudopetiolate condition. However, I have not seen the completely elaminate pseudopetiolate condition in these moss-

Aphid Infestation and Its Effects on Translocation in Polytrichum commune

Polytrichum commune Hedw. is susceptible to attack by Myzodium modestum Hottes, a moss aphid. Scanning electron micrographs indicate that aphids feed by insertion of needlelike stylets into moss gametophores. Liquid scintillation analysis indicates that aphids draw upon labelled tracers following 14C-sucrose treatment of leaves on infested plants. Between 17 and 38% of translocated label can be detected in 2-15 feeding aphids within 4 hr. Localized infestation on a single gametophore within otherwise uninfested plant groupings reduces the flow of label to remote sites (i.e., the shared underground rhizome plus connected neighbors, where allocation falls from 4 to 1% or lower), and alters labelled allocation patterns near the infested site. These data indicate that infesting Myzodium aphids 1) divert nutrients from the food conducting tissues of moss gametophores, and 2) alter the normal source-to-sink flow within moss turfs. Host-specific aphids are widely distributed in the plant kingdom. Most feed on the phloem of flowering plants (Hodkinson & Hughes 1982). A few show specificity for mosses as primary or secondary hosts (Gerson 1982; Moran 1989; Miiller 1973; Patch 1938). The mosses that these aphids attack usually possess an internal food conducting tissue system similar in structure and function to phloem (Eschrich & Steiner 1967; H6bant 1977; Reinhart & Thomas 1981; Thomas et al. 1988). Unfortunately, the procedures so far employed for collection of aphids specific for these mosses provide little information about feeding behavior or the plant tissues from which nutrition is derived. The only reported observation of aphid-moss feeding is that of Melaphis rhois on gametophores of Haplocladium microphyllum (Moran 1989). Feeding was inferred by the presence of droplets of honeydew. One of the objectives of this study was to determine whether Myzodium modestum, an aphid that infests Polytrichum commune gametophores (Miiller 1973), taps nutrients from the translocate flow of its bryophyte host. Scanning electron microscopy was employed to determine the means by which these aphids feed. Radioactive tracers were employed to follow the movement of nutrients from the translocate stream. Another objective was to determine whether aphids can significantly alter translocation patterns in mosses. Aphid infestation of flowering plants is capable of preventing translocate from reaching host roots and of inducing changes in the partitioning of assimilates in affected host shoots (Hawkins et al. 1987; Wu & Thrower 198 1). These changes are presumably of benefit to aphids, but can also markedly alter growth and physiology of the plants that they infest. Our study was designed in part to determine whether infestation of P. commune by M. modestum aphids alters translocation patterns in ways comparable to those observed in flowering plants. MATERIALS AND METHODS Colonies of Myzodium modestum Hottes on Polytrichum commune Hedw. turfs were observed between July and September 1982-1988, in a beech-maple-white pine forest near Webster, Maine. Quick-frozen, critical-pointdried, and gold-coated specimens were observed under an AMR-1000 scanning electron microscope set at an accelerating voltage of 5 kV. Some specimens were preserved in ethanol and sent to Dr. Manya Stoetzel, Beltsville Ag0007-2745/91/1-4$0.55/0 This content downloaded from 157.55.39.208 on Fri, 14 Oct 2016 04:16:38 UTC All use subject to http://about.jstor.org/terms 2 THE BRYOLOGIST [VOL. 94

Ecological and Physiological Investigations in Continental Antarctic Cryptogams: I. Vegetation Pattern and its Relation to Snow Cover on a Hill Near Casey Station, Wilkes Land

Summary The vegetation of the summit region of a small ice:free hill in the inner part of the east-Antarctic Bailey Peninsula, Windmill Islands, was recorded by 105 releves along various transects. It was analysed by the Braun-Blanquet phytosociological method, by a divisive polythetic procedure and tested by an ordination analysis. An epipetric Usnea sphacelata- and a Rinodina olivaceobrunnea -moss turf community were described as distinct communities and additionally a transient community. The vegetation is highly dependent on the extension and duration of a shallow snow cover, because snow is the main water source for the poikilohydrous cryptogams. This was shown by recording regularly the changes of snow cover in 5 quadrats of the summit region. The photophilous, wind- exposed vegetation of this hill resembles ecologically that of high arctic and alpine regions. The dominance of Neuropogon species is characteristic of the Antarctic and also the Andine region, in equivalent arctic-alpine communities Umbilicaria species are the most prominent element. The epibryic and epigeic Rinodina olivaceobrunnea -moss turf community has no identical counterpart in the arctic and alpine region.

Pollen and spores transport into the Antarctic

Pollen deposition in a 7 cm thick moss turf (Polytrichum juniperinum) from a site in Admiralty Bay (King George Island, maritime Antarctic zone) and in three cushions of Schistidium antarcticum (1–3 cm thick) from Bailey and Clark Peninsula (Wilkes Land, Greater Antarctica) were investigated. Twenty-four pollen and spore taxa were identified from a total of 1094 grains in the sample from Admiralty Bay. By contrast, the 3 samples from Wilkes Land contained only 10 grains (5 taxa). While the former sample was poor in lichen-mycobiont spores the latter revealed very many. Pollen deposition appears to be a good indicator of direction and frequency of immigration of cryptogamic propagules. It seems that the presence of cryptogamic species in the maritime Antarctic zone is predominantly the result of long-distance transport from neighbouring South America and a selection by climatic factors. The low frequency of pollen in Wilkes Land indicates a separation of this part of Antarctica from propagule exchange with other continents and the cryptogams of most of the Antarctic continent may represent a largely relictual flora which survived in ice-free refugia.

Responses of Ranunculus sabinei and Papaver radicatum to removal of the moss layer in a high-arctic meadow

Within the High Arctic, vascular plants of small size often grow in dense turfs of moss. The effect of moss removal on vascular plant growth was examined over a 2-year period for Ranunculus sabinei and Papaver radicatum. Aboveground non-repoductive parts of flowering R. sabinei were significantly (p < 0.05) larger for individuals in moss removal and moss clipped treatments than those in control plots. Similar but nonsignificant differences were found for nonflowering individuals of R. sabinei. Papaver radicatum had significantly (p < 0.05) larger aboveground, nonreproductive biomass in moss removal and replacement plots than in the moss clipped treatment and the controls. We suggest that the responses of Ranunculus sabinei to moss clipping or removal and of Papaver radicatum to moss removal and moss replacement are examples of the interaction between moss and vascular plants in relation to microsite conditions. Moss turf provides more soil moisture during drought periods as well as higher levels of nutrients. Moss removal results in warmer and more aerated soils. We interpret these results as commensalism rather than competition.

Environmental factors influencing decomposition rates in two Antarctic moss communities

Rates of disappearance of dead material of Polytrichum alpestre and Chorisodontium aciphyllum from a moss turf community and of Drepanocladus uncinatus, Calliergon sarmentosum and Cephaloziella varians from a moss carpet community, measured using litter bags over 2 years, were 1.5% year-1. Decomposition potential, estimated using loss in tensile strength of cotton strips inserted into the different bryophytes on the two sites, was also low. Ranking the five plant species in order of decomposition potential, from highest to lowest, gave D. uncinatus, C. aciphyllum, C. sarmentosum, P. alpestre and C. varians. The time taken for the tensile strength of the cotton strips at depths of 1–3 and 4–6 cm beneath the surface to decline by 50% varied from 1–2 years under the first two species to 3–4 years beneath the last two species. The main causes of these slow rates were low temperatures, short active season and low pH. Differences in decomposition between species, sites and with depth were related to temperature, nutrient status, water content and anaerobic conditions. Variation in anaerobic conditions beneath D. uncinatus, C. sarmentosum and C. varians in the moss carpet resulted in wide variation of decomposition rate beneath these species and with depth beneath C. varians. The peat in the moss turf was aerobic and experienced higher temperatures, but the average decomposition rate was no higher than in the moss carpet, because the peat was of a poorer quality and had a lower pH.

Microscale pattern of vascular plant distribution in two high arctic plant communities

Microscale pattern is of crucial importance in determining the distribution of vascular plants in the extreme environments of the High Arctic. Point-quadrat analysis of the distribution of the vascular plants in a mesic cryptogam–herb meadow and a xeric Puccinellia barren found a nonrandom distribution of vascular species. Most species were found growing in moss turfs versus crustose lichen or bare soil surfaces in the meadow and in desiccation cracks in the barren. Two species showed an opposite distribution pattern in the meadow indicating that incipient niche differentiation occurs in the High Arctic. Quadrat sampling showed that seed distribution was random in the meadow and only slightly skewed toward cracks in the barren. Microsites appeared to be crucial to the seedling establishment and adult distribution pattern for Papaver radicatum but less important for Ranunculus sabinei. Microclimate analyses showed that soil temperatures were higher, wind speeds were lower, soil moisture content was greater, and nitrate levels were higher in the microsites usually preferred by plants.

Energy partitioning in the Antarctic collembolan Cryptopygus antarcticus

Abstract. 1. Consumption, production and assimilation rates were determined for two age groups of Crypropygus antarcticus to give an estimate of energy utilization, and to investigate low temperature adaptation in its energy partitioning.2. Feeding selectivity shown in laboratory preference tests was supported by gut analysis of field animals from contrasting sites. Although moulting rate was not significantly affected by food type, rates of growth were slowest and mortality highest when fed on a non‐preferred substrate.3. Both a radio labelling and a more direct method for measuring dry weight consumed gave similar results for Cvpropygus feeding on algae. The consuniption rate for animals when feeding on algae was lower than that on moss peat. The assimilation efficiency for immature animals feeding on algae was 46% and for mature animals was 19%; the values when feeding on moss peat were 7% and lo%, respectively, The net production efficiency ranged from 35%(inimatures) to 13% (matures) and was similar on both substrates.4. Food consumption exceeded assimilation over the range 2.5–10°C, but the two converged from 2.5 to 0°C. Immature Cryptopygus maintained a net positive energy balance over 0–10°C, whilst below 1S°C respiration exceeded assimilation for mature individuals.5. An estimate of the annual dry matter consumption (7 g m‐1 y‐1) by Ctypropygus in a moss turf at Signy Island agrees with one based on respiration data alone (Davis, 1981). The consumption at an alga‐dominated site was c. 26 g m‐2 y‐l, and Crypropygus may have a locally limiting effect on net priniary production at such sites.

Biomass and Respiration of Nematode Populations in Two Moss Communities at Signy Island, Maritime Antarctic

1. The biomasses of free-living soil nematodes from a moss turf and a moss carpet, two contrasting bryophyte ecosystems in the maritime Antarctic, are analysed and compared with other tundra studies. 2. The mean annual live-weight biomass of nematodes from the moss turf ranged from 105 to 355 mg m-2, that from the moss carpet showed less variation being from 222 to 236 mg m 3. Seasonal variations from a low winter biomass to a high summer value are explained by seasonal fluctuations in soil temperature. 4. Total annual nematode population respiration at the two sites was very similar, being 1726.1 1? 02 m2 d-1 in the moss turf and 1761.0 il ?2 m-2 d-1 in the moss carpet. 5. Nematodes form an important part of the soil fauna and are responsible for 16% and 35% of the metazoan respiration in the moss turf and carpet respectively. 6. The short Antarctic summer and generally low temperatures limit nematode production to 0.95 and 1.12 kcal m2 yr-1 at the two sites.

Structure and Function of Two Antarctic Terrestrial Moss Communities

Two bryophyte—dominated communities in the maritime Antarctic are analyzed in terms of the transfer and standing crops of organic matter within them. A moss turf dominated by Polytrichum alpestre and Chorisodontium aciphyllum and a moss carpet composed of Calliergon sarmentosum, Calliergidium austro—stramineum, and Drepanocladus uncinatus with the liverwort Cephaloziella varians were investigated at Signy Island, South Orkney Islands. Biomass, respiration, and production data for the primary producers (mosses, lichens, liverworts, and algae), for the fauna (Protozoa, Rotifera, Tardigrada, Nematoda, Acari, and Collembola), and for the microflora were synthesized, and annual rates of consumption, egestion, assimilation, and production were derived. The two communities showed similar levels of productivity, trophic structure, and efficiencies of organic matter transfer, but different Collembola and Acari standing crops, turnover of mosses, and accumulation of dead organic matter. These features are discussed in relation to the role of biotic and abiotic variables in determining community structure and function.

Peat respiration and decomposition in Antarctic terrestrial moss communities

Oxygen uptake by the peat of two Antarctic bryophyte communities (a moss turf and a moss carpet) is converted to organic matter loss and used to derive the rate of decomposition. The decay rates obtained in this way are evaluated in two mathematical models which simulate the accumulation of dead organic matter (DOM) in the communities from the litter production and decomposition rate. Litter production, the extent of DOM accumulations at present on the sites and mean decomposition rates (i.e. fraction of standing crop lost per year) were 409 g m-2 year-1, 33.5 kg m-2 and 0.017 g g-1 year-1 in the moss turf and 392 g m-2 year-1, 29.6 kg m-2 and 0.010 g g-1 year-1 in the moss carpet respectively (all weights expressed as dry weight). Aerobic decomposition rate declined with depth in both communities. From the model's predictions it is suggested that the observed decay rate was too high in the moss turf and too low in the carpet. Possible reasons for this are discussed and suggestions made for future work.

Annual Periodicity of Incremental Growth in the Moss Polytrichum commune

In the temperate moss species Polytrichum commune Hedw. field studies demonstrated that growth segments which are formed by changing patterns of leaf morphology are repeated annually. Evidence for exceedingly smallscale microhabitat variability in available water was found in the scattered distribution of desiccated stems in space and time, throughout the population under study. Moss turfs were extremely sensitive to disturbance which apparently altered the water-regulating capacity of the normally unbroken moss canopy. Mortality rates reported were undoubtedly elevated due to disturbance of the moss canopy during the course of this investigation. The last few years have witnessed a growing interest in the study of demography of plant populations (cf. Harper & White, 1974 for review). Allied to this interest has been a need to identify plant species in which ages of individual plants may be easily determined on the basis of direct morphological assessment. Formation of annual growth rings in woody perennials is the best known example of this type of interpretable morphological periodicity. Tree ring analysis has frequently been used in the study of historical events within a region or as an aid in the construction of management schedules for commercially harvested stands. Only recently, however, has this type of information been used in the construction of life tables for the study of the dynamics of natural forest stands (Hett & Loucks, 1971, 1968; Hett, 1971). Even less information is available for perennial herbs, which in general lack reliable morphological criteria for assigning age. Work by Tamm (1948, 1956, 1972a, 1972b) on life histories of woodland herbs relied exclusively upon mapping of individuals over years of observation in permanent plots. Similar methodology was employed in the recent work of Sarukhain and Harper (1973), in which successive cohorts of three Ranunculus spp. were mapped and observed over a three year period in order to elucidate the differences among the three species in life history patterns. Several herbaceous plant species do, however, possess sound morphological cues upon which a life history analysis may be structured. For example Kerster (1968), 1This work was done in partial fulfillment of requirements for the degree of Doctor of Philosophy, Yale University, 1974. It was supported in part by USPHS Predoctoral Training Grant in Developmental Biology and a Sigma Xi Grant-in-Aide of Research. I would like to thank the New Haven Water Company for access to their land. 2 Department of Biology, University of Utah, Salt Lake City, Utah 84112. This content downloaded from 207.46.13.115 on Sat, 08 Oct 2016 05:20:07 UTC All use subject to http://about.jstor.org/terms 1975] WATSON: GROWTH PERIODICITY IN POLYTRICHUM 415

A classification of terrestrial vegetation near McMurdo Sound, continental Antarctica

Eleven plant sociations are reported from the McMurdo Sound region of continental Antarctica, and they are grouped in the Alga, Fruticose and Foliose Lichen; Crustaceous Lichen; and Short Moss Turf and Cushion subformations of the Antarctic Non-vascular Cryptogam Tundra formation. Their inclusion necessitated only minor modification of a vegetation classification developed in the maritime Antarctic.The most widespread vegetation consisted of sparsely developed communities of turf- and cushion-forming mosses in habitats ranging from dry cinder slopes to sand and gravel in seepage areas and by meltwater streams. The bryophyte colonies seldom exceeded 4 cm in depth, and although total plant cover within the communities locally reached 85%, it was more frequently under 5%. The Sarconeunim association appeared to tolerate more arid conditions than the Bryum association, whose communities occasionally merged with algal sociations occupying certain of the streams. Exposed rock habitats normally supported at most small scattered thalli of crustaceous lichens, well-developed lichen communities being rare.